Thank you for clarifying.
If she's asking for some time from you, try to have her tell you how long is she talking about? A few weeks, a couple of months, etc. and what exactly would she be doing during this time - go to counseling, engage in self introspection, and so on.
It would be helpful if she is able to let you know what is she expecting from you during this period of time.
Her unhappiness does not have to be related to the marriage or you. It could be a case of early mid life crisis, feeling depressed and projecting that onto you, feeling unfulfilled in her life and thinking that she's missing something.
You could ask her if she may be interested in couple's counseling or if she's thinking of working on these issues (whatever they are if she knows ) on her own.
You can honor her wish for time and she'd need to be specific about how this time will be used. If you resist, she may use that against you and blame you for her "unhappiness" And, you can speak to her and ask her to think of how this is going to effect the children as well in the long run.